When constructing x-ray detectors, the main challenges are to achieve high detection efficiency, enable a modular arrangement of detectors and/or make sure packaging and wiring is possible so that the detector can be efficiently produced. It is furthermore beneficial if all requirements can be met at the same time, which is a challenge since in part the requirements contradict each other. For example the wiring and packaging required for a modular arrangement often means you have to sacrifice active detector area such that the geometrical efficiency is reduced.
Furthermore the x-ray detector in most cases has to be integrated with an anti-scatter collimator or grid to eliminate scatter from the object and/or between detector modules. It is also desirable that sensitive integrated circuits are protected from direct radiation since a high accumulated dose could negatively impair the functioning of the circuits.
At the same time each detector module and anti-scatter grid should preferably be accurately aligned to the incident x-rays from the source.
State-of-the art detectors in for example Computed Tomography are based on a scintillator converting the x-rays to visible light that is detected by a dedicated photo diode that integrate the signal for many x-rays. The photo diode is connected to integrated circuits that digitize the produced current and this value is used to calculate grey scale values displayed in the x-ray image. A one-dimensional or two dimensional anti scatter grid is placed on top of the scintillators and diodes. To avoid cross talk a trench separates each scintillator-diode assembly. The anti-scatter collimator is positioned to match the trenches in order to minimize any dead area. There are several ways to solve the packaging and wiring challenges: to connect the diode to the integrated circuit, to provide power and data transmission. There are good examples how these challenges can be addressed. One example is disclosed in reference [1] where a fully modular arrangement is presented that can be tiled in two dimensions. Another example for an interconnect and packaging method is presented in reference [2] where an elastomer conducting contact is configured to provide a high-voltage anode signal.
The last years a lot of research focus both in academia and in industry has been focused on how to provide x-ray detectors with higher spatial and contrast resolution. One of the most promising ways to achieve this is through photon counting spectral detectors. So far these imaging detectors are only available for mammography in early breast cancer detection, see reference [3], but the next use may be in Computed Tomography. Two different solutions have emerged, one based on heavy detector elements such as CdTe or CdZnTe presented for example in reference [4] and another based on Silicon as detector material as outlined in reference [5].
In a Silicon detector assembly such as outlined in reference [5] the challenges in detection efficiency and modularity are very different compared to assemblies with heavy elements as detector material since the Silicon detectors need to be much longer (around 30-40 times) in the direction of the incoming x-rays in order to absorb a major fraction of the x-rays. This means the geometry and mechanical constraints are very different.